Centrifuge at maximum speed for 10 mins at room temperature and aspirate out 400 µl of top layer.Transfer top aqueous layer into sterile 2-ml microcentrifuge tube (3).Discard bottom layer.DO NOT PICK UP ANY PRECIPITATE!!!

(Optional)Measure out 400 µl of PCA solution into sterile 2-ml microcentrifuge tube (3).Close the tube tightly and gently mix the contents by inverting the tube.Centrifuge at maximum speed for 3 mins at room temperature and aspirate out the top layer.Transfer top aqueous layer into sterile 2-ml microcentrifuge tube (4).Discard bottom layer.This helps remove any residual proteins.